Apparatus and method for modulation of a curl-free magnetic vector potential field

ABSTRACT

Apparatus for producing and modulating a magnetic vector potential field having a substantially curl-free component. Detection and demodulation of the curl-free component of the magnetic vector potential field using a Josephson junction device are described of the curl-free magnetic vector field. Examples of modulation of the curl-free magnetic vector field suitable for detection and demodulation by the Josephson junction device are disclosed.

RELATED APPLICATIONS

Apparatus and Method for Transfer of Information by Means of a Curl-FreeMagnetic Vector Potential Field invented by Raymond C. Gelinas, Ser. No.198,324, filed on Oct. 20, 1980 and assigned to the same assignee asnamed herein.

Apparatus and Method for Distance Determination by Means of a Curl-FreeMagnetic Vector Potential Field invented by Raymond C. Gelinas, Ser. No.198,326, filed on Oct. 20, 1980 and assigned to the same assignee asnamed herein.

Apparatus and Method for Direction Determination by Means of a Curl-FreeMagnetic Vector Potential Field, invented by Raymond C. Gelinas, Ser.No. 198,553 filed on Oct. 20, 1980 and assigned to the same assignee asnamed herein.

Apparatus and Method for Demodulation of a Modulated Curl-Free MagneticVector Potential Field, invented by Raymond C. Gelinas, Ser. No.198,325, filed on Oct. 20, 1980 and assigned to the same assignee asnamed herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the transfer of information by meansof an electromagnetic field, and more particularly to the apparatus fordemodulation of the curl-free magnetic vector potential field.

2. Description of the Prior Art

It is known in the prior art to provide systems for the transfer ofinformation utilizing electromagnetic fields which are solutions toMaxwell's equations. The information transfer systems include apparatusfor generating modulated electromagnetic fields and apparatus fordetecting and demodulating the generated electromagnetic field. Examplesof the prior type information transfer systems include radio andtelevision band-based systems, microwave band-based systems and opticalband-based systems.

The maxwell equations, which govern the prior art transfer ofinformation by electromagnetic fields can be written: ##EQU1## where

E is the electric field density,

H is the magnetic field intensity,

B is the magnetic flux density,

D is the electric displacement,

J is the current density and

ρ is the charge density.

In this notation, the bar over a quantity indicates that this is avector quantity, i.e., a quantity for which a spatial orientation isrequired for complete specification. The terms CURL and DIV refer to theCURL and DIVERGENCE mathematical operations and are denoted symbolicallyby the ∇x and ∇ mathematical operators respectively. Furthermore, themagnetic field intensity and the magnetic flux density are related bythe equations B=μH, while the electric field density and the electricdisplacement are related by the equation D=εE. These equations can beused to describe the transmission of electromagnetic radiation through avacuum or through various media.

It is known in the prior art that solutions to Maxwell's equations canbe obtained through the use of electric scalar potential functions andmagnetic vector potential functions. The electric scalar potential isgiven by the expression: ##EQU2## where

φ(1) is the scalar potential at point 1,

ρ(2) is the charge density at point 2,

γ₁₂ is the distance between point 1 and 2, and the integral is takenover all differential volumes.

The magnetic vector potential is given by the expression ##EQU3## where

A(1) is the vector potential at point A,

ε_(o) is the permittivity of free space,

C is the velocity of light,

J(2) is the (vector) current density at point 2,

γ₁₂ is the distance between point 1 and point 2 and the integral istaken over all differential volumes.

The potential functions are related to Maxwell's equations in thefollowing manner. ##EQU4## where GRAD is the gradient mathematicaloperation and is denoted symbolically by the ∇ mathematical operator.

8. B=CURL A

where A can contain, for completeness, a term which is the gradient of ascalar function. In the remaining discussion, the scalar function willbe taken to be substantially zero. Therefore, attention will be focusedon the magnetic vector potential A.

In the prior art literature, consideration has been given to thephysical significance of the magnetic vector potential field A. Themagnetic vector potential field was, in some instances, believed to be amathematical artifice, useful in solving problems, but devoid ofindependent physical significance.

More recently, however, the magnetic vector potential has been shown tobe a quantity of independent physical significance. For example, inquantum mechanics, the Schroedinger equation for a (non-relativistic,spinless) particle with charge q and mass m moving in an electromagneticfield is given by ##EQU5## where

h is Planch's constant divided by 2π,

i is the imaginary number √-1, φ is the electric scalar potentialexperienced by the particle,

A is the magnetic scalar potential experienced by the particle and

ψ is the wave function of the particle.

Thus, devices such as the Josephson junction device quantum mechanicaleffects can be used to detect the presence of curl-free magnetic vectorpotential. In order to provide a system for transfer of informationusing the curl-free magnetic vector potential, apparatus fordemodulating the modulated curl-free vector potential field must bedesigned to provide for the physical differences between the typicalelectromagnetic field generally used in communications and the curl-freemagnetic vector potential field.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide animproved system for transfer of information.

It is a further object of the present invention to provide apparatusdemodulation of a modulated curl-free vector potential field.

It is a more particular object of the present invention to provideapparatus for detection of the curl-free vector potential field andapparatus for analyzing output signals of the detection apparatus.

It is another particular object of the present invention to provideapparatus for demodulating the output signals of a Josephson junction,the Josephson junction used to detect the curl-free magnetic vectorpotential field.

SUMMARY OF THE INVENTION

The aforementioned and other objects are accomplished, according to thepresent invention, by apparatus for detecting a magnetic vectorpotential field having a substantial curl-free component (i.e., CURLA=0) and by apparatus coupled to the detection apparatus fordemodulation of signals produced by the detection apparatus. An exampleof a detector of curl-free magnetic vector potential fields is theJosephson junction. The intention of the curl-free magnetic vectorpotential field on the Josephson junction results in a change in thephase of the current, I_(JJ), flowing through the junction. Thedemodulation system converts the Josephson junction current phasechanges into quantities directly related to the modulation of the field.

These and other features of the present invention will be understoodupon reading of the following description along with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the procecure for determininga magnetic vector potential at a point.

FIG. 2 is a schematic diagram illustrating the generation of a curl-freemagnetic vector potential field using an infinite solenoid.

FIG. 3 is a schematic diagram illustrating the generation of a curl-freemagnetic vector potential field using a toroidal configuration.

FIG. 4a is a cross-sectional diagram of a Josephson junction.

FIG. 4b is a perspective drawing of a Josephson junction.

FIG. 5 is a diagram of the current flowing in a Josephson junction as afunction of field perpendicular to the junction surface.

FIG. 6 is a schematic diagram of a system for using a magnetic curl-freevector potential field for transmission of information.

FIG. 7 is a schematic diagram of aparatus for demodulating a weakcurl-free magnetic vector potential field.

FIG. 8 illustrates the method of operation of apparatus for demodulatinga weak curl-free magnetic vector potential field.

FIG. 9 is a schematic diagram of apparatus for demodulating a strongcurl-free magnetic vector potential field.

FIG. 10 illustrates the method of operation for demodulating a strongamplitude-modulated curl-free magnetic vector potential field.

FIG. 11 illustrates the method of operation for demodulating a strongcurl-free magnetic vector potential field with arbitrary modulation.

FIG. 12 is a schematic diagram of apparatus for producing a modulatedcurl-free magnetic vector potential field.

FIG. 13 demonstrates some examples of modulation of a curl-free magneticvector potential field.

DESCRIPTION OF THE PREFERRED EMBODIMENT

1. Detailed Description of the Figures

Referring to FIG. 1, the method of determining the magnetic vectorpotential field A(1) (i.e., at point 1) is illustrated. Referring toequation 6, the contribution by the differential volume element at point2, dv(2), having a current density J(2) associated therewith is given by##EQU6## To obtain equation 6, equation 10 must be integrated. Equations6 and 10 are valid where J is not a function of time.

Referring to FIG. 2, an example of current configuration producing asubstantial component of curl-free magnetic vector potential field isshown. Conductors carrying a current I are wrapped in a solenoidalconfiguration 21 extending a relatively great distance in bothdirections along the z-axis. Within solenoid 21, the magnetic fluxdensity B=CURL A is a constant directed along the z-axis with a value##EQU7## where n is the number of conductors per unit length. Outside ofthe solenoid, it can be shown that the components of A 23 are ##EQU8##where a is the radius of the solenoid. It can be shown that CURL A=0 forthe vector potential field.

Referring to FIG. 3, another example of a current geometry generatingmagnetic vector potential field with a substantial curl-free componentis shown. In this geometry the current carrying conductors are wrappeduniformly in toroidal configuration 31. Within the toroidalconfiguration, the magnetic flux B=CURL A and the magnetic flux iscontained substantially within the torus. In the region external to thetorus, B=CURL A=0 and the orientation of the magnetic vector potentialfield is parallel the axis of the torus.

Referring to FIG. 4a and FIG. 4b, a detector capable of detecting thecurl-free component of the magnetic vector potential field is shown.This detector is referred to as a Josephson junction device. TheJosephson junction consists of a first superconducting material 41 and asecond superconducting material 42. These two superconducting materialsare separated by a thin insulating material 43. Superconducting material41 and super conducting material 42 are electrically coupled to otherapparatus by conductor 44 and conductor 45 respectively. Conductors 44and 45 can be superconduction materials and can be coupled together asshown by element 73 of FIG. 7, or can be coupled to other electricalelements. According to classical electromagnetic theory, the insulatingmaterial 43 will prevent any substantial conduction of electrons betweenthe two superconducting regions. However, quantum theory predicts, andexperiments verify that conduction can take place through the insulatingmaterial. The result of this conduction is a net current. ##EQU9## where

the magnitude of the current K and the phase δ_(o) are determined byintrinsic properties of the junction device.

e is the charge of the electron,

A is an externally applied magnetic vector potential,

ds is a differential element extending from one superconducting elementto the other superconducting element and

V is an externally applied voltage.

Referring to FIG. 5, the relationship of the Josephson junction devicecurrent I_(jj) as a function of externally applied magnetic vectorpotential field component A⊥ (i.e., the component perpendicular to theplane of the Josephson junction) is shown. The integral ∫A·ds as A isincreased results in a change of phase for I_(JJ). This change in phaseproduces the oscillating behavior for I_(JJ) as a function of magneticvector potential field perpendicular to the Josephson junction. Thisrelationship will hold as long as there is no externally applied voltageto the Josephson junction (i.e., V=0).

Referring next to FIG. 6, a system for the transfer of information usinga curl-free vector potential field is shown. Apparatus 60 is comprisedof a current source 64 and apparatus 65 configured to generate amagnetic vector potential field having a substantial curl-free componentusing the current from the currrent source. The magnetic vectorpotential field is established in the intervening media 61 and impingesupon a magnetic vector potential field detector 66. The property ofdetector 66 indicating the presence of a magnetic vector potential fieldis analyzed in apparatus 67 for information content.

Referring to FIG. 7 and FIG. 8, apparatus for demodulating a weakcurl-free magnetic vector potential field is illustrated. A weakcurl-free magnetic vector potential field is one for which the maximumamplitude of the field results in a relatively minor change in phase.The component perpendicular to Josephson junction 72 of curl-free vectorpotential field 71 A⊥ causes a change in the phase of Josephson junctioncurrent, I_(JJ) flowing in conductor 73. The change in current I_(JJ) isapplied through transfer means 74 to analog-to-digital converter 79. Theresulting digitalized signal is applied to storage analyzer and displaydevice 78. Device 78 has stored therein calibration data which relatesthe perpendicular component of appliance vector potential field A to theresulting Josephson junction current I_(JJ), (i.e., A=f(I_(JJ))). Inessence, the relationship illustrated by FIG. 5 is available to convertthe resulting Josephson junction current I_(JJ) to a quantity related toA. Thus it is possible to reconstruct the magnitude of the impingingmagnetic vector field potential and the modulation can be extractedtherefrom.

Referring next to FIG. 9, the schematic diagram of apparatus fordemodulation strong curl-free vector potential fields is shown. Thestrong field apparatus is used when the impinging magnetic vectorpotential field results in multiple phase changes for the Josephsonjunction current. The weak field apparatus has response too slow todetermine effectively the magnitude of the vector potential field. Thechange in component perpendicular to the Josephson junction 72 of thecurl-free vector potential field causes a change in the Josephsonjunction current I_(JJ) flowing in conductor 73. Transfer means 74causes a signal related to I_(JJ) to be applied to overdriven amplifier91. The output signal from amplifier 91, essentially a series of squarewaves, is applied to differential circuit 92. The output signal fromcircuit 92 is applied to counter 93 and the resulting counts are storedin storage, analyzer and display circuit 94. The result of using thisapparatus on an amplitude modulated sinewave signal is shown in FIG. 10.In FIG. 11, the result of using this apparatus to analyze a generalcurl-free vector potential field signal is shown.

2. Operation of the Preferred Embodiment

When the curl-free magnetic vector potential carries information, thefield must vary in a manner so that the information is transmittedtherewith. No mention has been made in the previous discussion of theeffect of varying the current source. It will be clear, however, thatthe finite field propagation velocity will cause a delay between achange in the curl-free magnetic vector potential field produced by thegenerator of the field and the detection of that change by the detectorlocated at a distance from the generator. However, these delay effectsare not important for the practice of this inventin and will be ignoredin this discussion. With respect to curl-free vector potential fieldgenerating apparatus, any limitation on the upper limit of generatedfrequency components imposed will be the result of parameters impactingrapid changes in the current. Thus parameters such as inductance canprovide a limit to ability to impose high frequency modulation on thevector potential field.

With respect to the media between the field generating apparatus and thefield detecting apparatus, two effects are important. First as impliedby equation (1) ##EQU10## or ##EQU11## Therefore, as modulation isimposed on the vector potential field, the change in the vectorpotential field will produce an electric field intensity. The electricfield intensity will produce a flow of current in conducting material ora temporary polarization in polarizable material. With respect tomaterials demonstrating magnetic properties, the bulk magneticproperties are responsive to the magnetic flux density B. However,B=CURL A=0 for the curl-free vector potential field component.Therefore, the interaction of the curl-free magnetic vector potentialfield is weaker in magnetic materials than is true for the generalmagnetic vector potential field. Media effects and especially theconductivity of the intervening media will provide a mechanism delayingthe achievement of steady state condition for the curl-free magneticvector potential field ##EQU12## and thus causing a media limitation onfrequency. A curl-free magnetic vector potential field can beestablished in materials that are not capable of transmitting normalelectromagnetic radiation. The media delay problem can be compensatedfor by lowering the frequency spectrum of the modulation on thecurl-free magnetic vector potential field.

With respect to the detector, the Josephson junction can be constructedto provide responses of sufficiently high frequency so that this elementof the system is not typically a factor limiting frequency ofinformation transfer.

As indicated in equation 12, the effect of the application of a vectorpotential field to a Josephson junction, in the absence of a voltageapplied to the junction, is to change the phase of the sine functiondetermining the value of the junction current I_(JJ). The excursionsfrom zero magnetic vector potential field can be analyzed and adetermination made of the modulation applied to the field. When avoltage is applied to the Josephson junction, oscillation occurs in theI_(JJ) as will be seen from the Vdt term of equation 12. The applicationof an external vector potential field causing the phase of theoscillation to change. By monitoring the phase change in the Josephsonjunction oscillations from the modulation of the vector potential fieldcan be inferred.

When a Josephson junction is used in the detection apparatus, themodulated curl-free magnetic vector potential field results in changesin phase for the current which can be analyzed in a manner depending onwhether the field influencing the detecting apparatus is a strong fieldor a weak field.

Considering first the weak curl-free magnetic vector potential field,the modulation for this field can be accomplished by calibrating thedetecting apparatus using the relationship of FIG. 5 so that a givencurrent from the Josephson junction can be interpreted in terms of thedetected vector potential field.

Considering next the demodulation of a strong curl-free magnetic vectorpotential field, the use of digital techniques provides a convenientmethod for analysis. In essence, four pulses are generated for eachchange of phase of 360°. Pulses will (except for noise signals) begenerated only when the magnetic field is varying. Thus, several formsof modulation can be utilized. The length of time a vector field varies,the relative slope of the changing vector field, and the relative heightof the vector potential field can all be used as modulating methods.

The presence of pulses can indicate that the vector field is changing,the relative number of pulses during a period of vector field canindicate the relative magnitude of the change, and the relative densityof pulse during a vector field change can indicate the relative vectorfield slope.

In addition, an amplitude modulated signal can be similarly demodulated.In the case of amplitude modulation, however, there can be little reasonto use the carrier frequency. To demodulate an amplitude-modulatedsignal, the time intervals of high (or low) density pulses can indicatethe frequency of the carrier. The number of pulses between the high (ordensity) pulse density region can indicate the relative modulationimposed on the signal.

Another method of detection of a magnetic vector potential fieldutilizes the property that ##EQU13## Thus, for example, by measuring thechanges in a material resulting from the application of the electricfield, the magnetic vector potential field causing the electric fieldcan be inferred.

Having reviewed the demodulation of a modulated curl-free magneticvector potential field, e.g. by a Josephson junction device, themodulation can be understood. When the detector provides a phase shiftas a result of a change in the field, the modulation device can consistof a device for regulating the current, the current being the mechanismgenerating the field.

The technique of modulating the field involves providing a relationshipbetween information unit and field property. Because the change in fieldstrength and the rate of change in the field strength can be determined,by providing a calibration standard, against which the change or rate ofchange can be measured against, information units can be identified oncethe calibration units are recognized on the modulation field. Thusmodulation can be a measure of the total change field strength during aperiod or measure of the rate of change as well as the more typicalamplitude and frequency modulatiion of a carrier frequency. The currentproducing the field in the curl-free magnetic vector potential field canbe controlled by a device for which the predetermined modulationtechnique has been implemented. Modulation can also be accomplished bymovement of the field generating apparatus.

Many changes and modifications in the above-described embodiment of theinvention can, of course, be carried out without departing from thescope thereof. Accordingly the scope of the invention is intended to belimited only by the scope of the accompanying claims.

What is claimed is:
 1. Apparatus for generating a modulated curl-freemagnetic vector potential field A comprising:a configuration of at leastone conducting element adapted to generate a magnetic vector potentialfield surrounding said conducting element configuration when current isapplied to said conducting element configuration, a substantial portionof said vector field having a curl-free magnetic vector potential A(defined by CURL A=0) component; a current source coupled to saidconducting element configuration for applying current thereto; andmodulating means for controlling current from said current source. 2.The apparatus of claim 1 wherein said conducting element configurationhas a toroid configuration.
 3. The apparatus of claim 1 wherein saidmodulating means produces a change in said current in a predeterminedmanner in response to each of a plurality of information units to betransmitted by said curl-free magnetic vector potential field.
 4. Theapparatus of claim 1 wherein said modulating means produces a rate ofchange in said current in a predetermined manner in response to each ofa plurality of information units to be transmitted by said curl-freevector magnetic vector potential field.
 5. A method of generating amodulated curl-free magnetic vector potential field A comprising thesteps of:(a) configuring at least one conducting element to produce amagnetic vector potential field when current is applied to said at leastone conducting element said magnetic vector potential field (A) having asubstantial component of said magnetic vector potential field subject tothe condition that CURl A=0 (i.e., ∇x A=0), (b) applying a current tosaid at least one conducting element; (c) modulating said current inaccordance with information desired to be transmitted by said curl-freemagnetic vector potential field.
 6. The method of generating a modulatedcurl-free magnetic vector potential field of claim 5 wherein said atleast one conducting element is configured in the form of a toroid.